The instant invention relates to high voltage shunt reactors for high voltage electrical power transmission lines, and more particularly, to a coreless reactor contained within a magnetic shell for use on high voltage power transmission lines.
High voltage shunt reactors are employed on electrical power transmission lines, normally operating in the 138 kilovolt to 1300 kilovolt range, where they are usually connected from line to ground. These devices are an essential element in such power transmission systems in the control of line voltage, and of line impedance and, therefore, also power flow. Reactors are installed at terminal substations as well as at strategic points along the transmission line, and are designed to provide a constant reactance, or a reactance which changes with voltage, or in some cases, a reactance which can be changed by a suitable switching operation.
Conventional, high voltage reactors closely resemble conventional power transformers in their physical construction. In the conventional design, the reactance characteristics are achieved by providing a number of thin "air gaps" in the main leg of the magnetic core, which is surrounded by a coil. These are not really air gaps but are filled with some non-magnetic material, chosen to meet the mechanical and electrical requirements of the reactor design. The reactance gaps are often filled with pieces of stone, cut and ground to the desired shape or may be filled with other commonly-used insulation material, for example, mineral oil combined with cellulosic material such as craft paper, paper composites and wood. The thermal and mechanical stresses present in a high voltage reactor and the limitations of these conventional materials have presented a limitation on the design of high voltage reactors. Another major practical limitation is in the design of the pole faces of the core where they meet the reactance gaps. Large losses have been associated with this region in the conventional machines, due to stray flux entering the adjacent coil parts and heating them.